You could always consider that it may have been what my brother calls Divine Inspiration that brought it out of Newton; in those few moments it took him to write it down, he was "At One" with whatever higher being he believed in or you might believe in.

Just a suggestion. I know there are times when I listen to Mozart, Beethoven and others, including some folk, when I feel the music is absolutely sublime and directly channelled from someone's heart which was fully open to receiving when they wrote it. My brother leads a fairly miserable life, but when he sets aside his self-pity and starts in on his compositions, he goes to another realm. The music he writes in no way reflects his circumstances at the time; as far as he is concerned it is divinely inspired. It certainly sounds like it to a lot of folks. Perhaps that was the case with Newton.

Imagine having a flash of clarity like that which would inspire such a beautiful song. It would be difficult to sustain that and probably wouldn't be very healthy for one to do so, anyway.

Well, that's my metaphysical two cents worth...:-)